Technical Field
The disclosure in generally relates to a semiconductor structure and method for fabricating the same, and more particularly to a memory device and method for fabricating the same.
Description of the Related Art
Recently, there is an increasing need for the more excellent memory device, and various types of the three-dimensional (3D) memory devices are provided, such as a surrounding-gate vertical-channel (SGVC) 3D NAND memory device having a multi-layer structure. This type of the 3D memory device can achieve higher storage capacity and has more excellent electrical characteristics, for example, having better data retention reliability and higher operating speed.
The typical SGVC 3D NAND memory device includes a plurality of stacking structures having a plurality of insulating layers and a plurality of conducting layers alternatively stacked on a substrate, and a plurality of memory layers and a plurality of channel layers longitudinally penetrating through the stacking structures. The intersections of each of the channel layers and each of the memory layers define the NAND memory cells. The NAND memory cells are connected by the channel layers to form NAND memory strings. The NAND memory strings electrically contact with the ground layer under the stacking structure through the ground selecting line (GSL) transistor.
Since the conventional ground layer is formed of the poly-silicon material, the resistance is relatively higher, and it is easy to produce the IR drop effect. To improve this drawback, metal contact structures are generally disposed between the memory blocks longitudinally penetrating through the stacking structure, to guide the current to the ground. However, the arrangement of the metal contact structures compresses the layout space of the memory strings, and further reduces the storage space of the SGVC 3D NAND memory device.
Therefore, there is a need of providing an improved memory device and method for fabricating the same to obviate the drawbacks encountered from the prior art.